Duke starting forward Ryan Kelly has been resting his right foot for four weeks now, and coach Mike Krzyzewski still doesn’t know when — or if — he’ll return.

"It's almost been a month now, and there is no new news,” Krzyzewski told ESPN on Tuesday night. "He's getting better, but he still can't do anything weight-bearing yet.”

Duke's Ryan Kelly last played on Jan. 5. (AP Photo)

Kelly attempted to play through the pain but could go only 18 minutes against Wake Forest on Jan. 5 and 19 minutes against Clemson on Jan. 8. He’s been in a walking boot since.

Kelly’s absence has had a profound effect on the Blue Devils. Duke was undefeated and ranked No. 1 in the country with him playing power forward, stretching defenses by shooting 52.1 percent from 3-point range and scoring 13.4 points per game.

Without Kelly, Duke has lost its only two games against ranked opponents -- by eight at N.C. State on Jan. 12 and a humbling 27 points at Miami on Jan. 23.

Duke’s next challenge is a rematch against N.C. State on Thursday night.

The Blue Devils are 4-2 without Kelly and have won three straight, including a 20-point win vs. Maryland and a 19-point road win at Florida State last weekend.

All-American candidate Mason Plumlee is confident that Kelly will return at some point this season, even if he doesn’t know when.

"The Maryland game was the first one that we hit our stride without Ryan," Plumlee said Tuesday on SiriusXM's Inside College Basketball. "Since then, we've been playing well. It took us a little bit, but I think now we're in a good place.

"We've seen (Kelly) without his air-sock cast on and doing a little more rehab. But we don't know when we're going to have him back. I would hope we'd have him back by the end of the ACC season, but with these kind of injuries, you never really know."